Polymers and oligomers having carbamate functional groups have been used in a variety of curable coating compositions. Carbamate-functional polymers offer many advantages in these coating compositions, such as resistance to environmental etch and resistance to scratching and marring. One kind of carbamate-functional polymer described in the art is addition-type polymers. One known method for preparing a carbamate-functional polymer is to transesterify a hydroxy-functional acrylic polymer with a carbamate compound. Tin compounds, specifically tin oxides, are typically used for the transesterification or transcarbamation of hydroxy-functional acrylate polymers with carbamate compounds, such as alkyl carbamates. "Transcarbamation" as used in this application is defined as a process where a carbamate group is put on a monomer or polymer at a hydroxyl site.
Tin compounds used as transesterification catalysts, however, are known in the art to cause yellowing and to be deleterious to weathering in humid conditions. Another problem with the use of tin compounds is an undesired increase in the molecular weight of the polymer undergoing transesterification. This is thought to be a result of side reactions that occur as the transesterification reaction continues to run. Additionally, tin catalysts cannot be used for transesterification reactions when there is any acid present in the reaction medium. It would thus be desirable to find other catalysts with improved properties that may be employed for the transesterification or transcarbamation of hydroxy-functional acrylic polymers with carbamate compounds.
The present invention provides a method for preparing carbamate-functional polymers including providing a hydroxy-functional polymer and then reacting a carbamate compound with the hydroxy-functional polymer in the presence of a transcarbamation catalyst. A carbamate-functional polymer is thus formed. The transcarbamation catalyst may be a Bi(III) compound, Zr(IV) compound, or mixtures of these.
The present invention also provides a method for preparing carbamate-functional polymers including polymerizing in a reaction vessel at a temperature below about 150.degree. C. at least one hydroxy-functional monomer in the presence of a transcarbamation catalyst and a carbamate compound having 1 to 4 carbon atoms. An at least partially transcarbamated polymer is formed. The transcarbamation catalyst may be a Bi(III) compound, Zr(IV) compound, or mixtures of these.
The present invention further provides a method for preparing carbamate-functional acrylic polymers including polymerizing in a reaction vessel at a temperature below about 150.degree. C. at least one hydroxy-functional monomer in the presence of a transcarbamation catalyst and a carbamate compound having 1 to 4 carbon atoms. An at least partially transcarbamated polymer is formed. The transcarbamation catalyst may be a Bi(III) compound, Zr(IV) compound, or mixtures of these.
The present invention also provides a carbamate-functional polymer prepared by reacting a hydroxy-functional polymer with a carbamate compound in the presence of a transcarbamation catalyst. The transcarbamation catalyst may be Bi(III) compounds, Zr(IV) compounds or mixtures of these.